The importance of estuarine-derived carbon for the nearshore marine environment: studies on two. contrasting estuaries in South Africa

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1 SAMPLE MANUSCRIPT in AJAS FORMAT for uploading to website [See also The importance of estuarine-derived carbon for the nearshore marine environment: studies on two contrasting estuaries in South Africa Comment [c1]: Title should include the country in which the research was conducted PD Vorwerk 1 and PW Froneman 2 * 1 Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa; current address: SAEON, Grahamstown, South Africa Comment [c2]: Give only initials, not full names Comment [c3]: Always write "and" in full, not as "&" Comment [c4]: If a researcher has moved since the research was completed, give "current address" immediately after the "research address" 2 Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa * Corresponding author, w.froneman@ru.ac.za Abstract The food web structure within and adjacent to two permanently open estuaries with contrasting flow regimes along the south-eastern coast of South Africa was investigated in 2005, employing stable isotope analysis. In the Kariega Estuary carbon sources assimilated by the zooplankton are derived from riparian vegetation in the upper reaches and from salt marsh and submerged macrophytes in the lower reaches of the system. In contrast, within Comment [Ed.5]: Not more than 200 words, summarising the objectives, findings and conclusions of the research Comment [c6]: Always use 'passive voice' Comment [c7]: The year/s when the research was conducted should be mentioned the freshwater-dominated Great Fish Estuary the zooplankton appear to be sustained largely by allochthonous phytoplankton derived from freshwater inflow due to the interbasin transfer scheme. Estuarine-derived POM appears to be utilised only directly adjacent to the Kariega Estuary mouth. Keywords: Eastern Cape, flow regime, food web, isotope, linkages Comment [Ed.8]: Maximum of 8 keywords, listed alphabetically, separated by commas. Exclude words used in the title of the article

2 Introduction It has long been hypothesised that, due to the direction of flow through estuaries being predominantly seaward, the net transport of material (both biological and non-biological) is in a seaward direction (Allen 1996; Roegner and Shanks 2001). South African estuarine research has largely focused on the spatial and temporal variability in the Comment [Ed.9]: A broad overview of the subject in hand. Headings / sub-headings must not be numbered Comment [c10]: Do not put a comma between name and date biology within these systems. The main findings of estuarine research have highlighted the importance of freshwater inflow in determining the species composition and food web structure within these systems (Froneman 2001; Vorwerk et al. 2003; Gama et al. 2005). Comment [Ed.11]: References listed chronologically, separated by semi-colons. "et al." is NOT italicised This study was conducted within, and adjacent to, estuaries with contrasting freshwater flow regimes along the south-eastern coast of South Africa. The aim of the study was to assess the importance of estuarine-derived carbon to the nearshore marine ecosystem and to highlight any differences in the estuaries resulting from altered Comment [c12]: The research s objectives, and the hypothesis tested, should be clearly stated flow regimes. Materials and methods Comment [Ed.13]: Level 1 heading: bold; sentence case; line space above and below Study area The two estuaries studied are approximately 50 km apart along the Eastern Cape coast of South Africa (Figure Comment [Ed.14]: Level 2 heading: bold, italicised; sentence case; line space above but not below 1). They included the freshwater-deprived, marine-dominated Kariega Estuary and the freshwater-dominated Great Fish Estuary. The Kariega Estuary (33 41 S, E; Figure 1a) has a small catchment (686 km 2 ), whilst the Great Fish Estuary (33 30 S, E; Figure 1b) has a relatively large catchment ( km 2 ) Comment [Ed.15]: Note the format for longitude and latitude with several impoundments along its channel. Sample collection Due to the continuous recycling of nitrogen within estuarine ecosystems, this study focused only on carbon stable isotopes (Fry and Sherr 1984). The collection of POM samples involved transporting five litres of estuarine or marine water from each station to the laboratory for subsequent filtering through precombusted

3 (500 C) GF/F filters and the manual removal of any faunal matter, using a dissecting microscope. Zooplankton was collected monthly, from January to December 2005, from all sites during the day by a series of surface tows of a WP-2 net (0.05 m 2 mouth area) with a mesh size of 60 μm. Comment [c16]: Period or date when the research was undertaken should be mentioned Stable isotope analysis Sample analysis was conducted in an online Carlo-Erba NA1500 preparation unit and δ 13 C determination was performed in a MAT 252 stable light isotope mass spectrometer. Merck gelatine was used as an internal standard, calibrated against several IAEA reference materials. The results were expressed as δ 13 C signatures in units of parts per thousand ( ) relative to the Pee Dee Belemnite solution.. Statistical analysis The post hoc Tukey test was performed to identify whether there were any significant differences in the isotopic signatures at different locations within the different biotic groups. The STATISTICA software package (Version 6.0; Statsoft, Inc.) was utilised to conduct the analysis. Results Comment [c17]: Do not include Discussion text here. The Kariega Estuary and adjacent marine environment Primary producers and particulate organic matter (POM) The riparian vegetation sampled demonstrated a δ 13 C ratio of between and 21.07, while the salt marsh and littoral vegetation covered a greater range from to (Figure 3, Table 1). The most depleted δ 13 C signatures recorded were those for the salt marsh plant Sarcocornia perennis ( ) and the riparian plant Sideroxylon inerme ( ). The most enriched signatures were recorded for eelgrass, Zostera Comment [c18]: ALL scientific names are italicised capensis ( ), and the salt marsh plant, Sporobolus virginicus ( ) (Table 1, Figure 3).

4 Consumers (filter feeders and zooplankton) The marine filter feeders collected were either Pyura stolonifera (red bait) or an unidentified sponge species. A post hoc Tukey test identified two significantly different groupings, with the δ 13 C ratios of the filter feeders near Comment [Ed.19]: Level 3 heading: italics; sentence case; line space above (unless immediately below a Level 1 heading [see above]), no line space below the estuary mouth being more depleted than those further away along the coast (Table 3)... A Tukey test identified two significantly different groups, the estuarine copepods and the marine copepods (Table 4). Discussion Previous studies have demonstrated that the main carbon source assimilated by primary and secondary Comment [c20]: Not to be combined with 'Results' text consumers within South African estuaries appears to be dependent on the volume of fresh water flowing into the system (de Villiers 1990; Jerling and Wooldridge 1995). In those systems characterised by sustained freshwater inflow, phytoplankton appear to be the main carbon source utilised by the zooplankton (Jerling and Wooldridge 1995). The Kariega Estuary Stable isotope analysis within the Kariega Estuary indicated two distinct carbon pathways that were spatially separated from one another. The δ 13 C signatures of the POM in the upper reaches of the estuary were closely linked to the δ 13 C signatures of the group of plants comprising the riparian vegetation, whereas in the lower reaches the δ 13 C signatures of POM were closely related to those of Spartina maritima, Zostera capensis and Sporobolus virginicus (Figure 3)... The Great Fish Estuary As in the Kariega Estuary, the vegetation sampled within the Great Fish Estuary grouped into a highly depleted group ( to ) and a group comprising the relatively enriched S. virginicus ( ) (Figure 4). The highly depleted group comprised riparian vegetation and two species of reeds, as well as the salt marsh plant S. perennis...

5 Acknowledgements The authors would like to express their appreciation to Joe Sparks, Rhodes University, for field assistance. The running expenses of this study were funded by Rhodes University and the Water Research Commission. The stable isotope analysis was conducted by the Department of Archaeology, University of Cape Town. References Bligh E, Dyer WJ A rapid method of total lipid extraction and purification. Canadian Journal of Biochemistry and Physiology 37: de Villiers CJ Aspects of the biology of the infaunal bivalve mollusc Solen cylindraceus in the Kariega Estuary. PhD thesis, Rhodes University, South Africa. Comment [Ed.21]: Note AJAS style. See for reference exemplars. Do NOT import References direct from Reference Manager, because that system imposes incorrect formatting on them Comment [c22]: Journal name given in full, and italicised Comment [c23]: Volume number not in bold. Issue number not quoted Comment [c24]: Full stop required Odum EP The status of three ecosystem level hypotheses regarding salt marshes: tidal subsidy, outwelling and the detritus based food chain. In: Kennedy VS (ed.), Estuarine perspectives. New York: Academic Press. pp RSA (Republic of South Africa) National Water Act (Act No. 36 of 1998). Government Gazette, South Africa 398(19182). Comment [c25]: Give full name, plus acronym Whitfield AK, Wood AD Studies on the river-estuary interface region of selected Eastern Cape estuaries. WRC Report No. 756/1/03. Pretoria: Water Research Commission.

6 Tables Table 1: δ 13 C signatures ( ) of primary producers collected from the Kariega Estuary in April Different grouping letters indicate significantly different groups (Tukey test; p < 0.05, df = 8) Species Habitat type Mean δ 13 C SD Max. Min. Grouping according to Tukey test Sarcocornia sp. Salt marsh A Sideroxylon inerme Riparian C Sporobolus Salt marsh D Rhus sp. Riparian C Chenolea diffusa Salt marsh BC Schotia affra Riparian C Portulacaria affra Riparian CD Spartina maritima Salt marsh D Zostera capensis Littoral D Comment [c26]: Use MS Word 'Table' format, each Table on a separate page, with all Tables compiled into one file Comment [c27]: Numbered with Arabic numeral Comment [c28]: Legend must contain information describing "what, where and when" concerning the data given in that Table Comment [c29]: No full stop required

7 FIGURES Figure 1: Locations of the two study estuaries, the Kariega Estuary (a) and the Great Fish Estuary (b). Hatched areas indicate salt marshes. The causeway forming the upper limit of the Kariega Estuary is indicated by a dotted line Comment [Ed.30]: Each Figure on a separate page, all figures compiled into a single file. Use colour ONLY where necessary, so as to avoid hard-copy cost. See the NISC website ( for examples of figure style Comment [c31]: Write as "Figure", not "Fig." Comment [c32]: Numbered with Arabic numeral Comment [c33]: No full stop required.